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Photoactivated biological processes as quantum measurements.
We outline a framework for describing photoactivated biological reactions as generalized quantum measurements of external fields, for which the biological system takes on the role of a quantum meter. By using general arguments regarding the Hamiltonian that describes the measurement interaction, we identify the cases where it is essential for a complex chemical or biological system to exhibit nonequilibrium quantum coherent dynamics in order to achieve the requisite functionality. We illustrate the analysis by considering measurement of the solar radiation field in photosynthesis and measurement of the earth's magnetic field in avian magnetoreception
Continuous Measurement of a Non-Markovian Open Quantum System
Continuous quantum measurement is the backbone of various methods in quantum
control, quantum metrology, and quantum information. Here, we present a
generalized formulation of dispersive measurement of a complex quantum systems.
We describe the complex system as an open quantum system that is strongly
coupled to a non-Markovian environment, enabling the treatment of a broad
variety of natural or engineered complex systems. The system is monitored via a
probe resonator coupled to a broadband (Markovian) reservoir. Based on this
model, we derive a formalism of Stochastic Hierarchy Equations of Motion (SHEM)
describing the decoherence dynamics of the system conditioned on the
measurement record. Furthermore, we demonstrate a spectroscopy method based on
weak quantum measurement to reveal the non-Markovian nature of the environment,
which we term weak spectroscopy.Comment: Published version, the section on continuous state tomography will be
published in a separate manuscrip
Collective Effects in Linear Spectroscopy of Dipole-Coupled Molecular Arrays
We present a consistent analysis of linear spectroscopy for arrays of nearest
neighbor dipole-coupled two-level molecules that reveals distinct signatures of
weak and strong coupling regimes separated for infinite size arrays by a
quantum critical point. In the weak coupling regime, the ground state of the
molecular array is disordered, but in the strong coupling regime it has
(anti)ferroelectric ordering. We show that multiple molecular excitations
(odd/even in weak/strong coupling regime) can be accessed directly from the
ground state. We analyze the scaling of absorption and emission with system
size and find that the oscillator strengths show enhanced superradiant behavior
in both ordered and disordered phases. As the coupling increases, the single
excitation oscillator strength rapidly exceeds the well known Heitler-London
value. In the strong coupling regime we show the existence of a unique spectral
transition with excitation energy that can be tuned by varying the system size
and that asymptotically approaches zero for large systems. The oscillator
strength for this transition scales quadratically with system size, showing an
anomalous one-photon superradiance. For systems of infinite size, we find a
novel, singular spectroscopic signature of the quantum phase transition between
disordered and ordered ground states. We outline how arrays of ultra cold
dipolar molecules trapped in an optical lattice can be used to access the
strong coupling regime and observe the anomalous superradiant effects
associated with this regime.Comment: 12 pages, 7 figures main tex
Perfect initialization of a quantum computer of neutral atoms in an optical lattice of large lattice constant
We propose a scheme for the initialization of a quantum computer based on
neutral atoms trapped in an optical lattice with large lattice constant. Our
focus is the development of a compacting scheme to prepare a perfect optical
lattice of simple orthorhombic structure with unit occupancy. Compacting is
accomplished by sequential application of two types of operations: a flip
operator that changes the internal state of the atoms, and a shift operator
that moves them along the lattice principal axis. We propose physical
mechanisms for realization of these operations and we study the effects of
motional heating of the atoms. We carry out an analysis of the complexity of
the compacting scheme and show that it scales linearly with the number of
lattice sites per row of the lattice, thus showing good scaling behavior with
the size of the quantum computer.Comment: 18 page
News Sentiment and the Investor Fear Gauge
This note examines the relationship between aggregate news sentiment and changes in the implied volatility index (VIX). A significant negative contemporaneous relationship between changes in VIX and news sentiment is discovered. The relationship is asymmetric whereby changes in VIX are larger following the release of negative news items
Minimum construction of two-qubit quantum operations
Optimal construction of quantum operations is a fundamental problem in the
realization of quantum computation. We here introduce a newly discovered
quantum gate, B, that can implement any arbitrary two-qubit quantum operation
with minimal number of both two- and single-qubit gates. We show this by giving
an analytic circuit that implements a generic nonlocal two-qubit operation from
just two applications of the B gate. We also demonstrate that for the highly
scalable Josephson junction charge qubits, the B gate is also more easily and
quickly generated than the CNOT gate for physically feasible parameters.Comment: 4 page
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